1. Field of the Invention
The present invention relates to a fly back transformer (to be called "FBT" below) which generates a high voltage to supply it to a TV or a monitor. Particularly, the present invention relates to a focus unit of an FBT, which is installed on a side of the FBT, so that the focus and screen voltages can be adjusted. More specifically, the present invention relates to a focus unit of an FBT, in which the filling and curing of an insulating resin are eliminated. That is, a ceramic substrate with a resistor pattern formed thereon is installed within a cover through which an actuation knob of the focus unit passes. A slider is installed at an end of a volume shaft, and the volume shaft is formed integrally with the actuation knob, while a central contact of the slider contacts to a central terminal which is formed within the case, the case being facingly coupled with the cover. Further, a variable contact of the slider contacts to the resistor pattern of the ceramic substrate, so that a volume control can be carried out. Further, the ceramic substrate which is installed within the focus unit and on which the resistor pattern is printed is installed within the cover of the focus unit, and separated from an FBT case within which bobbins are installed. Therefore, the filling and curing of an insulating resin becomes needless.
2. Description of the Prior Art
In the generally known conventional FBT, the low voltage and high voltages bobbins generate a high voltage, and this high voltage is supplied through an anode cable to a cathode ray tube. Under this condition, the focus unit which is installed on a side of the FBT case varies the focus voltage and the screen voltage through a volume slider.
This conventional focus unit of the FBT is constituted as shown in FIG. 1. That is, a rotating piece 54 is installed within a main body 52 of the focus unit 51, and is connected to a focus and screen adjusting handle 53. On the top of the rotating piece 54, there is installed a slider 55 which has two contact points 56 and 56'. A substrate 58 on which a circuit pattern 57 having variable and central contact points 57a and 57b is printed is installed in such a manner that the contact points 57a and 57b are connected to the contacts 56 and 56' of the slider 55. From the substrate 58, there protrudes an output pin 59, and the substrate 58 is insulated by coating an insulating resin 60.
In the conventional focus unit 51 constituted as described above, if the focus and screen voltages are to be varied, the focus and screen adjusting handle 53 is turned. Then the slider 55 is rotated together with the rotating piece 54 to vary the voltages. Under this condition, the slider 55 has two contacts 56 and 56', and one of them (56) is connected to the variable contact 57a of the circuit pattern 57 of the substrate 58, thereby stepping up or down the focus and screen voltages. Meanwhile, another (56') of the contacts is connected to the central contact 57b, so that an output can be drawn through a resistor.
However, in this conventional focus unit 51, the slider 55 which is installed above the handle 53 has two contacts 56 and 56' for stepping up or down the focus and screen voltages. Further, the circuit pattern 57 of the substrate 58 has variable and central contacts 57a and 57b, so that these contacts can be made to be connected to the contacts 56 and 56'. Thus the structure is very complicated, and the contacts might not be electrically connected, these being serious disadvantages.
Further, the substrate 58 having the circuit pattern 57 is disposed at the rear side of the focus unit, and therefore, the circuit pattern 57 is disposed near to the bobbins from which the high voltage is drawn. Therefore, the insulating characteristic is very weak. In order to overcome this problem, the substrate 58 is coated with an insulating resin, this being a troublesome task.